1. Field of the Invention
The present invention relates to novel direct dyes for preparing non-oxidative colorants for keratin fibers, for example hair, silk or wool.
2. Description of Related Art
The dyeing of human hair is currently subjected to the most varied trends. Whereas previously hair was dyed primarily to cover gray areas for an extended period of time, today an increasing demand exists for integration of the hair color into current fashion and the use of it as an expression of a subject's personality.
As before, two methods are available for the dyeing of hair. One of these methods is oxidative hair dyeing which gives long-lasting dyeing results. The other method consists of non-oxidative tinting which as a rule is more gentle than oxidative dyeing but also less durable. Non-oxidative colorants are advantageous particularly when the customer wants to change the color shades more frequently and at the same time wants to avoid a deterioration of hair quality from frequent exposure to oxidants considering that it is possible to apply non-oxidative (“direct”) colorants under very gentle conditions. Because in the case of tints the colorations can be weakened gradually with every hair washing, such colorations normally withstand at the most 10 to 15 hair washings, depending on the product used and the kind of hair. Customers often make use of precisely these properties so that they can later apply new color shades to achieve a different coloring result. For both dyeing methods, the oxidative and the non-oxidative, achieving a high color density on the hair with only minor skin staining is particularly desirable.
Cationic dyes with arylazo groups or heteroarylazo groups as well as anthraquinones and naphthoquinones were found to be particularly well suited for use as tinting agents, the cationic group possibly being delocalized or localized. In this regard we mention, for example, the widely used “Arianor®-Dyes” which not only have good coloring properties but also cause only very minor skin staining. Most “Arianor®-Dyes” are cationic azo dyes, and only the blue dye (“Arianor® Steel-Blue”) is a naphthoquinone derivative. A particular problem of these “Arianor®-Dyes” is that the dyes are sometimes washed out at different rates so that, if one or more dyes are washed out more intensely, the color shade can change in an uncontrollable manner.